The find proves once again that the deep sea still holds many secrets for us.

In the so-called Midnight Zone – the part of the ocean that resides between 1000 and 4000 meters below the surface of the water – scarlet jellyfish are not a rare sight. The jellyfish – belonging to the genus Atoll – are frequent. In addition to their eye-catching color, they can also be recognized by the fact that they are each equipped with one thin tentacle that is many times longer than their other tentacles.

New species

So there was a great surprise when, years ago, in Monterey Bay – a bay off the coast of California – researchers stumbled upon a scarlet jellyfish without that one, extremely long tentacle. Their interest was immediately aroused. And the result of this has recently appeared in the magazine animals: a research article in which they describe the special jellyfish in detail and show that it belongs to a species unknown to us until recently.

special stomach

The jellyfish has the name Atolla reynoldsi and is – like other jellyfish of the same genus – characterized by a scarlet, grooved umbrella-shaped swimming bell. Besides the absence of that one long tentacle distinguishes A. reynoldsi also distinguishes itself from other jellyfish by its special stomach which is shaped like a Greek cross (a cross with four arms of equal length). What is also unique about A. reynoldsi, is that it often coils its tentacles slightly, making the tip of it appear to curl (which is the picture below). We are also not familiar with the soft projections on the edge of the swimming bell from other jellyfish from this genus.

Image: © 2014 MBARI.

Big

What is also striking is that A. reynoldsi is quite large compared to other jellyfish of the genus; the swimming bell of the largest individual that the researchers could lay hands on was about 13 centimeters in diameter. With that, A. reynoldsi one of the largest jellyfish in its genus.

Rare
A. reynoldsi has so far only been found in Monterey Bay and lives there about 1000 to 3200 meters below the water’s surface. For now, all indications are that the jellyfish is quite rare; between April 2006 and June 2021, researchers have been able to identify only ten individuals belonging to the newly described species.

Atolla reynoldsi. Image: © 2018 MBARI.

More discoveries
A. reynoldsi will certainly not be the last asset to it Atoll– be gender; researchers have their eye on two more scarlet jellyfish that also have to do without that strikingly long tentacle, but are slightly different from A. reynoldsi† It is therefore expected that these two species are still unknown to us. At the moment, however, there is too little information available to describe these jellyfish – which have only been spotted a few times to date – and to find out whether they deserve a specific name of their own. If they are described in the future, this could also have consequences for A. reynoldsi† Because both candidate jellyfish species have, just like A. reynoldsi about a cruciform stomach and that, combined with the lack of a long tentacle, could lead researchers to choose this – along with A. reynoldsi – to be placed in a separate genus. Before doing so, however, it is not only those two jellyfish species that need further study; also other species from the Atollgenus must then be further investigated both genetically and morphologically to determine what defines this genus and whether A. reynoldsi and the species yet to be described belong therein. In anticipation of that, researchers have opted for now to A. reynoldsi for the time being in the Atollto place gender.

A. reynoldsi was discovered by scientists of the Monterey Bay Aquarium Research Institute (MBARI). The institute has been searching for new species in Monterey Bay and the surrounding area for years and with success; in the past 34 years they have described more than 225 new species. A. reynoldsi is the latest example of this, but there are undoubtedly more to follow, according to researcher George Matsumoto. “These remarkable new jellyfish show just how much we can still learn about the deep sea. We learn something new on virtually every dive into the depths of Monterey Bay.” Mapping all that unknown is fascinating. But it is also a race against time. “The deep sea and the animals that live there face increasing threats,” said Matsumoto. “And we can’t protect life in the deep sea if we don’t understand it first.”